1. Field of the Invention
The present invention relates to an aspheric plastic lens and a mold for manufacturing the same. In the aspheric plastic lens, a two-stage step portion is formed on a rib surface thereof such that optical performance is not influenced by burrs formed when the aspheric plastic lens is injection-molded. Then, the horizontal coupling between lenses in a lens barrel is achieved.
2. Description of the Related Art
With the recent development of mobile terminals such as portable phones and Personal Digital Assistants (PDAs), the mobile terminals provide a phone call function and are used as multi-convergence devices. The most representative of the multi-convergence devices is a camera module. The resolution of the camera module changes from 30,000 pixels (VGA) to 800,000 pixels.
Generally, compact camera modules (CCMs) are applied to various IT devices. Recently, products having the CCMs to meet consumers' various tastes are increasingly put on the market.
Such camera modules are manufactured by using image sensors and lenses as main parts, the image sensors including charge coupled device (CCD) and complementary metal oxide semiconductor (CMOS) image sensors. Incident light transmitted through the lens is condensed by the image sensor and is stored as data in the memory. The stored data is displayed as an image through a display medium, such as liquid crystal display (LCD) or PC monitor.
Recently, with the development of digital technologies, the improvement of image compression/decompression technologies, and the technical improvement of peripheral devices of multimedia products, lenses for the mobile cameras have been continuously developed and researched for slim profile and miniaturization. Further, the development of an aspheric plastic lens having a mega-pixel resolution is being accelerated, in which various aberrations can be controlled. Because of the aberrations, the shape of an object is deformed by an influence of light having a variety of wavelengths, the light being incident when the object is imaged.
The aspheric plastic lens is pressed between a pair of pin cores so as to be injection-molded. The plurality of lenses are sequentially laminated inside a cylindrical lens barrel, thereby forming a lens optical system ranging from a VGA quality to a mega quality.
While the aspheric plastic lenses are laminated and combined inside the lens barrel, the lenses can be tilted or floated so that a defective lens unit including the optical system can be manufactured. A lens having such a defect cause and a lens molding structure therefor will be described briefly with reference to FIG. 1.
FIG. 1 is a sectional view of a conventional aspheric plastic lens. As shown in FIG. 1, the conventional aspheric plastic lens 100 includes a spherical surface portion 110 formed in the center thereof and a flat rib 120 formed on the outer peripheral edge of the spherical surface portion 110. The spherical surface portion 110 includes a curved surface having a predetermined curvature, on which reflected light of an object is incident.
The rib 120 of the aspheric plastic lens 100 has burrs 130 formed to vertically project on the upper and lower surfaces thereof at a different height.
When the conventional aspheric plastic lens 100 having such a structure is laminated and assembled into a lens barrel, the flat surface of the rib 120 should be closely attached on a receiving surface of the lens barrel such that the aspheric plastic lens 10 is horizontally assembled into the lens barrel. However, the burrs 130 formed at a different height on the upper and lower surfaces of the rib 120 come in contact with the receiving surface. Therefore, the lens 100 is tilted due to a height difference between the burrs 130.
As a result, it is difficult to adjust a focus in a lens unit to which the conventional lens 100 is assembled. Further, the reduction in image quality inevitably occurs due to the reduction in resolution.
The occurrence cause of the burrs 130 acting as a serious defect of the lens assembled into the lens unit will be examined with reference to a mold structure of FIGS. 2 and 3.
FIG. 2 is a diagram illustrating an injection mold when the conventional aspheric plastic lens is pressed, and FIG. 3 is a diagram illustrating the injection mold when the pressing is released.
As shown in FIGS. 2 and 3, the mold 200 for manufacturing the conventional aspheric plastic lens 100 is divided into a moving mold 210 and a fixed mold 220, which are symmetrically formed with each other. The moving and fixed molds 210 and 220 respectively include pin cores 211 and 221 and support cores 212 and 222 to which the pin cores 211 and 221 are coupled in the center thereof.
The respective pin cores 211 and 221 coupled to the support cores 212 and 222 of the moving and fixed molds 210 and 220 have electroless nickel-plated surfaces facing each other. As a half-molten lens 100′ is pressed between the surfaces, the aspheric plastic lens 100 of FIG. 1 is manufactured.
At this time, a minute clearance 230 is inevitably formed in the coupling portions between the support cores 212 and 222 and the pin cores 211 and 221, respectively. As the half-molten lens 100′ is injected, the clearance 230 is further enlarged by the injection pressure. As a result, the burrs 130 having a non-uniform height are inevitably formed on the upper and lower surfaces of the rib 120 of the aspheric plastic lens 100, as shown in FIG. 1.